The invention relates to a method for detecting a malfunction of an electric machine, in which a first variable influencing the torque of the electric machine is modulated, and also to a device for carrying out the method.
The torque of an electric machine can be influenced by a number of independent variables. Suitable measuring systems for directly determining a torque output or power output of electric machines are not normally provided in motor vehicle drivetrains. For example, the measurement of a drive-shaft torque is omitted for cost reasons. A desired torque output or power output of the electric machine therefore cannot be determined directly. In particular in the case of electric or hybrid vehicles, there may be a force-locked connection between an electric machine and the drive wheels of the vehicle, even when the vehicle is stationary. An undesired torque output or power output of an electric machine, for example due to a fault in the data communication or due to a component fault, may then cause a highly safety-critical movement of the motor vehicle, which goes against the driver's wishes.
In electric vehicles and hybrid vehicles, high electric machine outputs are used, and therefore high undesirable accelerations or decelerations may occur in the event of a fault. This leads to unstable driving dynamics, wherein, in particular with high decelerations, the driver hardly has the chance to counter-react. Should the electric machine supply an excessively small torque, this may also result in safety-critical driving situations. If, for example for regeneration, part of the total braking torque is to be taken over by the electric machine, it may be that said electric machine does not convert its proportion of braking torque however.
A method for fault detection in a drive arrangement is known from EP 1387459 A1, in which the drive arrangement comprises a polyphase electric motor and a convertor arranged downstream of the electric motor, in which the convertor controls the voltage at the individual phases of the electric motor, wherein the phase currents each run periodically in the phases of the electric motor. For fault detection of the electric motor, a number of phase currents of the electric motor are measured. Here, there is a sinusoidal modulation of the voltages of the electric machine.
Due to safety and monitoring reasons, it is thus necessary to have accurate knowledge of the correct torque output or power output of the electric motor and a possibility for rapid and effective intervention in the event of a fault.